1. Field of the Invention
This invention relates to the preparation of elastin hydrolyzates.
2. Description of the Prior Art
Elastin is the major component of elastic fibers found primarily in connective tissue in conjunction with collagen and polysaccharides. Major concentrations of elastin are found in blood vessels. Another source of elastin is in the ligaments, and more particularly, the ligamentum nuchae, prominent in the necks of grazing animals and in their hides. The ligamentum nuchae is a preferred source of elastin because of the high concentration of elastin therein.
Elastin is known to have a highly distinctive amino acid composition. Although similar to collagen in that one-third of the amino acid residues are glycine, elastin is rich in proline, and in contrast to collagen, elastin contains very little hydroxyproline, no hydroxylysine, and is very low in polar amino acids. Elastin is very rich in nonpolar aliphatic residues such as isoleucine, leucine, valine and alanine. Elastin, as present in mature animals, is highly cross-linked, therefore making it very difficult to solubilize. This dense cross-linking is attributable to the desmosine and isodesmosine residues which are highly functional and cross-link both intra- and interfibrillarly. It is believed that the desmosine and isodesmosine cross-linking gives the elastin fibers their elasticity. The desmosine residue can be represented by the structural formula: ##STR1## And the isodesmosine residue can be represented by the structural formula: ##STR2##
This highly cross-linked structure is extremely difficult to solubilize and purify, especially in the case of mature animals such as horses, cows and the like, which are aged and thus contain elastin which has an extremely high cross-link density.
Prior art methods of solubilizing elastin primarily include the use of elastases to hydrolyze the peptide linkages to provide an acceptable product.
Solubilized elastin has found utility in the cosmetic and pharmaceutical fields. However, its manufacture has been limited to small quantities and it is not necessarily of acceptable purities because of the enzymatic residue required for the hydrolysis.
Further, partially hydrolyzed elastins have been produced; however, the processing conditions for their production reduce the amount of desmosine and isodesmosine amino acid residues which are recovered in the elastin hydrolyzate. Therefor, many of the elastin hydrolyzates lose the primary elastin-characterizing amino acids, i.e. desmosine and isodesmosine. One particular method of producing elastin by nonenzymatic means is disclosed in "ELASTIN" by Berg et al. Cosmetics & Toiletries, Vol. 94, October, 1979.
Characteristically, elastin in its natural state in mature animals, and particularly the ligamentum nuchae, is present at a level of at least 3.5 combined desmosine and isodesmosine residues/1,000 amino acid residues. Thus, in order to produce a hydrolyzed elastin which retains the basic characteristics of elastin, it is necessary to recover substantially all of the desmosine and isodesmosine residues which are present in the starting material.
In accordance with the present invention, the method of producing a soluble elastin partial hydrolyzate in pure form is provided wherein the desmosine and isodesmosine residues are substantially recovered.